Sols of metal dialkyl dithiophosphates



United States Patent M 3,155,615 @l MEAAL BIALKYLZ Dlififlllltldl-HATESll. Qypters, Cranial-d, Ni, assignor to Essa Re: and EngineeringQomprmy, a corporation or is v o Dr wing. Aug. 1, W61, tier. No. 1285553it Claims. (Cl. 252--32fl} This invention relates to colloidal solscontaining metal dialkyl dithiophosphates, methods for their preparationand their use. Particularly, the invention relates to metal salts of lowmolecular weight dialkyl dithiophosphates prepared by neutralizingdialkyl dithiophosphoric acid in the presence of a detergent additive.

The use of metal dialkyl dithiophosphates as lubricating oil additivesis well known in the art. These materials are commercially used on awide scale because of their excellent properties in imparting extremepressure, anti-wear and rust prevention properties to minerallubricating oil. The active portions of the metal dialkyldithiophosphates are the metal, the phosphorus and the sulfur, while thedialkyl group primarily serves the purpose of solubilizing the materialinto the mineral oil. From an economic and efficiency standpoint, it ishighly desirable to make the dialkyl groups as small as possible andstill retain oil solubility. Normally, dialkyl dithiophosphates havingalkyl groups containing less than 6 carbon atoms are insoluble in themineral oil. However, it has recently been found that, by using certainselect mixtures of dialkyl groups of different carbon atom content,alkyl groups averaging less than 6 carbon atoms can be used. One suchdithiophosphate is prepared from mixed 0., and C alkyl groups, whileanother is prepared from mixed C and C alkyl groups. However, it has notheretofore been possible to prepare a stable oil solution of metaldialkyl dithiophosphate wherein the alkyl groups have an average carbonatom content of three or less. The present invention is based upon thediscovery that stable oil compositions containing dialkyldithiophosphates can be made where each alkyl group contains 3 carbonatoms or less, and which are efiective as lubrieating oil additives.Furthermore, the dithiophosphates of the invention are more effectivethan the present commercially available dithiophosphates since bypreparing the salt from lower molecular weight dialkyl groups, then agiven pound of material will contain a larger proportion of the metal,phosphorus and sulfur which are the effective portions of the molecule.

The metal dialkyl dithiophosphates of the invention are those whereineach alkyl chain contains 1 to 3 carbon atoms, while the metal may beany metal which forms a water-insoluble dialkyl dithioph'osphate, forexample: zinc, lead, cadmium, molybdenum, etc. Specific examples of suchdithiophosphates are zinc dimethyl dithiophosphate, lead diethyldithiophosphate, cadmium methylethyl dithiophosphate, molybdenumdi-isopropyl dithiophosphate, etc.

In order to obtain the colloidal sols of the dialkyl dithiophosphates ofthe invention it is necessary that said dithiophosphates be prepared inthe presence of a detergent additive. In general, additives soluble inthe oil and having good dispersing or detergent properties will beoperable. However, it is preferred to use those detergents which arelubricating oil detergents since such detergents erve the additionalfunction of maintaining cleanliness of the lubricated parts, e.g.,automotive engines.

The detergent additives which are preferred include petroleumsulfonates, synthetic alkyl aryl sulfonates, various alkyl phenates,alkyl phenate sulfides, phosphosulfurized olefin polymers, and variouscombinations of these additives. Following are specific descriptions ofseveral of the above types of detergent additives.

Patented Nov. 3, 1964 Petroleum sulionates generally used as lubricatingoil detergents are the oil-soluble alkaline earth metal salts of highmolecular weight sulfonic acids. These sulfonic acids are produced bythe treatment of petroleum oils of the lubricating oil range with fumingsulfuric acid and generally have molecular weights of about 300 to 700e.g., 350 to 500. Petroleum sulfonates are well known in the art andhave been described in numerous patents, e.g., US. 2,467,176.

Detergent sulfonates can also be derived synthetically from relativelypure alkyl aryl sulfonic acids having from about 10 to 33 carbon atomsper molecule. For example, sulfonated products of alkylated aromaticssuch as benzene, toluene, xylene, and naphthalene, alkylated witholefins or olefin polymers of the type of polypropylene,polyisohutylene, etc. can be used.

Specific examples of the above two types of sulfonates include calciumpetroleum sulfonate, barium petroleum sultonate, calcium di-C alkylbenzene sulfonate, barium di-C alkyl benzene sulfonate and calcium Calkyl benzene sulronate; wherein said di-C alkyl group is derived fromdiisobutylene; said (3,; alkyl group is obtained from tripropylene andsaid C alkyl group is obtained from tetraisobutylene.

The above sulfonates may be either neutral sulfonates, i.e., where thesulionic acid is neutralized with an equal mole equivalent amount ofmetal base, or the sulfonates may be of the so-called high alkalinitytype. In the latter case, additional metal base, in excess of thatrequired for simple neutralization, is reacted with the sulfonatesulfonic acid to form an alkaline product which can then be blown withcarbon dioxide to reduce its alkalinity and form a substantially neutralfinal product. Recent work has indicated that such so-called high a1-kalinity sulfonates are nothing more than dispersions of neutralsulfonates and a carbonate of the metal used which are believed to existin the form of colloidal sols. In any event, the term sulfonate as usedherein and in the appended claims includes both neutral sulfonates andso-called high alkalinity (or high metal content) sulfonates.

Phenate sulfides are also well known in the art and have been describedin numerous patents, for example, US. 2,451,345 and U.S. 2,362,289. Themore important of these materials are metal salts of phenol sulfideswhich may be typified by the following formula:

OH OH (HE wherein R represents an alkyl group, a is 0 to 4, b is O to 10and c is l to 5. The metal used to form the phenate may be aluminum,cobalt, chromium, sodium, lead, tin, etc., or the alkaline earth metalsas calcium, barium, strontium and magnesium. Each alkyl group cancontain 5 to 20, e.g., 7 to 12 carbon atoms, either straight or branchedchain. Specific examples of the phenate sul fides include bariumtertiary octyl phenol sulfide, calcium tertiary octyl phenol sulfide,barium-calcium tertiary 'octyl phenol sulfide, barium tertiary amylphenol sulfide, calcium tertiary amyl phenol sulfide, barium nonylphenol sulfide, etc. High alkalinity (i.e., high metal content) phenatesulfides are also included in the above description. These materials areprepared by reacting the phenol sulfide with an excess of metal base andthen neutralizing the basic product, generally by C0 blowing.

The phosphosulfurized olefin materials are also well known in the art.These materials are prepared by reacting an olefin or an olefin polymerwith P 8 A specific material of this type used in an example of theinvcntion was P 5 treated polybutene about 1100 molecular weight.

The products of the invention are prepared by forming the metaldithiophosphate in situ in oil in the presence of a detergent additive.This can be accomplished by a number of methods.

A preferred method is as follows:

(1) Form a first solution of the dithiophosphoric acid in a firstoil-immiscible solvent, (2) form a second solution of a metal compound,capable of reacting with the dithiophosphoric acid to form the desiredmetal dithiophosphate, in a second oil-immiscible solvent which ispreferably miscible with said first solvent, (3) slowly add the firstand second solution simultaneously to oil containing the detergent whilestirring to thereby slowly form metal dithiophosphate in the presence ofsaid detergent, (4) separate the first and second oil-immiscibleso'vents from the oil mixture and (5) recover the resulting sol of metaldithiophosphate in oil. An illustration of the foregoing method is asfollows: Dissolve the dialkyl dithiophosphoric acid in an alcoholic oraqueous solution. Form a second alcoholic or aqueous solution containinga salt of the desired metal, which salt is capable of reacting with thedithiophosphoric acid to form a metal salt of said dithiophosphoricacid. Simultaneously, the two solutions are added to an oil soultioncontaining the detergent additive. A metal salt of the dialkyldithiophosphoric acid will then be formed in situ in the presence of thedetergent additive. The alcohol and oil will separate into an alcohollayer and an oily layer. The alcohol layer is decanted and the metaldialkyl dithiophosphate will be in a colloidal form in the oily layerprotected by the detergent additive. The oily layer can be blown withnitrogen to remove any alcohol and finally the material can be heatedunder vacuum to remove any remaining volatile material. The material canalso be filtered. If the material is very viscous, then hexane or asimilar volatile diluent can be added to reduce the viscosity. Thematerial is then filtered, and the diluent then volatilized. The finaladditive will be a stable colloidal sol of the metal dialkyldithiophosphate and the detergent additive in oil. This additive canthen be added to other oil compositions to thereby impart detergency,anti-wear and other desirable properties.

Alcohols which can be used are those which will dissolve thedithlophosphoric acid and the metal salt, and which are low molecularweight so as to be readily volatile. Such alcohols will include methyl,ethyl, n-propyl, isopropyl, etc. Alcohols are also preferred since theywill readily separate from the oil-detergent mixtures and will notemulsify during mixing with the detergent.

The metal salts which are suitable for reaction with thedithiophosphoric acid are those which are soluble in the volatilealcohol and which also result in volatile acids when the metal isremoved. Examples of such salts nclude acetates, chlorides, bromides,iodides, hypochlorites, etc.

While performed dialkyl dithiophosphoric acid can be used in carryingout the invention, said acid can be readily formed in situ in the lowmolecular weight alcohol. For example, alcohol is reacted with P 5 bysimple heating to form the acid as is well known in the art. By using alarge amount of the alcohol and a relatively small amount of the P 5then an alcohol solution of the dialkyl dithiophosphoric acid willresult.

The final oil compositions of the invention will comprise a majorproportion of lubricating oil, and 0.01 to 5.0 wt. percent of the metaldialkyl dithiophosphate and about 0.1 to wt. percent of detergentadditive (on an active ingredient basis). Preferred compositions willcontain about 0.1 to 2.0 wt. percent of said dithiophosphate and 1.0 to10 wt. percent of detergent additive. Concentrates containing 10 to 70wt. percent detergent additive and 2 to 14 wt. percent dithiophosphates,with the remainder oil, can also be prepared.

Various conventional lubricating oil additives may also be incorporatedin the compositions of the invention to form finished lubricants. Forexample, additives in the amounts of .1 to 10 wt. percent each can beadded, such as pour point dispersants, e.g. copolymers of vinyl acetateand alkyl fumarates; viscosity index (V.I.) improvers such aspolyisobutylene and polymethacrylates; anti-oxidants such as alkylphenols, bisphenols, sulfurizcd olefins; other detergents such as metalsulfonates or metal alkyl phenol sulfides, etc.

The invention will be further understood by reference to the followingexamples:

EXAMPLE I Solution A.-A first alcohol solution was prepared bydissolving 0.5 gram mol of zinc acetate in methanol to form a total of1,000 cc. of solution.

Solution .-A second alcohol solution was prepared by reacting 0.5 grammol of P 8 with 1000 cc. of 99% isopropyl alcohol, to form 1.0 gram molof di-isopropyl dithiophosphoric acid in 1000 cc. of solution.

Detergent addilive.-A lubricating oil detergent concentrate was used asa third component. This detergent consisted of about '70 wt. percentadditive and about wt. percent mineral lubricating oil. The additiveitself was prepared by heating a mixture consisting of about 40 wt.percent of a phosphosulfurized isobutylene, 30 wt. percent of an oilconcentrate of a high barium content tertiary oetyl phenol sulfide andabout 30 wt. percent of an oil solution containing wt. percent of a highbarium content sulfonate.

The phosphosulfurized polyisobutylene was prepared by reactingpolyisobutylene of about 1100 molecular weight with 15 wt. percent basedon the weight of polyisobutylene of P 8 at about 425 F. for about 8hours under a nitrogen atmosphere. The oil concentrate of the bariumtertiary octyl phenol sulfide consisted of about 43 wt. percent of saidsulfide and about 57 wt. percent of a mineral lubricating oil. Thebarium tertiary octyl phenol sulfide was of the high alkalinity typehaving an alkaline neutralization number of about and contained about 12wt. percent barium. The high barium sulfonate had a barium content ofabout 14 wt. percent, based on the weight of the sulfonate. The sulfonicacid portion of the sulfonate was prepared by alkylating benzene withpolypropylene, said sulfonic acid portion having an average molecularweight of about 440, and wherein 75 wt. percent of the sulfonic acidradicals had a molecular weight greater than 400. This sulfonate wasprepared by reacting neutral barium sulfonate with additional bariumhydroxide followed by neutralizing by bubbling carbon dioxide throughthe sulfonate.

Each of Solutions A and B was placed in a separate dropping funnel, andadded slowly and simultaneously to 500 grams of detergent additivecontained in a beaker, with constant stirring. After one hour all theingredients were added and stirring was stopped. The mixture thenseparated into an oily layer and an alcohol layer. The alcohol layer wasdecanted and the remaining oily layer was heated to a temperature ofabout 225 F. and blown with nitrogen for about one hour in order toremove any remaining alcohol and acetic acid formed during the reaction.The material was next heated for about two hours in a vacuum oven atabout C. operating at a pressure of mm. mercury to remove any remain ingvolatile material. The composition was then removed from the oven. Thisfinished colloidal sol product analyzed 1.42% zinc, 1.96% phosphorus and4.16% sulfur, and contained zinc diisopropyl dithiophosphate in a clearstable form.

, 5 EXAMPLE 11 Solution C.44.4 grams of P 8 was added over a period ofabout half an hour to 200 grams of refluxing methanol, boiling atatmospheric pressure. A clear alcohol solution of dimethyldithiophosphoric acid was thus formed.

Solution D.22 grams of (CH COO) Zn-2H O was dissolved in 200 grams ofmethanol.

One-half of Solution C (containing 31.6 grams of dimethyldithiophosphoric acid) was diluted with additional methanol to form atotal of 250 cc. of solution. All of Solution B and all of said 250 cc.of solution of the dimethyl dithiophosphoric acid were simultaneouslyadded from separate dropping funnels to 200 grams of detergent additive(same as in Example I) over a period of tWo hours and 40 minutes whilevigorously stirring. Stirring was then stopped and the mixture wasallowed to separate into an alcohol layer and an oily layer. The alcohollayer was decanted and discarded. The remm'ning oily bottom layer wasthen heated at 350 F. while stirring for a period of three hours whileblowing nitrogen through said layer. Next, hexane was added to the oilylayer to reduce its viscosity and the composition was filtered. Thehexane was then stripped oil by heating under vacuum. The remainingcolloidal composition analyzed: 2.09 wt.

percent zinc; 2.23 wt, percent phosphorus; 4.61 wt. percent barium and3.06 wt. percent sulfur, containing zinc dimethyl dithiophosphate in astable form.

EXAMPLE III Solution E.-The remaining half of Solution C from Example IIwas diluted with additional methanol to form a total of 250 cc. ofsolution.

Solution F.37.9 grams of (CH CO) Pb-3H O were dissolved in water to forma total of 250 cc. of solution.

All of Solutions E and F were simultaneously added from separatedropping funnels to 200 grams of detergent additive (same as in ExamplesI and II), over a period of 2.5 hours while stirring at roomtemperature. After all of said Solutions E and F were added, the mixturewas stirred for an additional hour. Stirring was then stopped and themixture was heated to 100 F. The water layer, which separated, wassiphoned from the mixture. The oily layer was heated to 225 F. whilestirring and blowing with nitrogen until no more volatile material cameoil. The mixture was then cooled to room temperature and filtered togive a clear stable colloidal sol additive which analyzed 9.0 wt.percent lead and 4.77. wt. percent sulfur, containing lead dimethyldithiophosphate.

EXAMPLE IV A lubricating oil composition was prepared by adding 4.7 vol.percent of the colloidal sol product of Example I to a multigrade SAEl0W-30 crankcase oil. The crankcase oil consisted of a mineral base oilcontaining a polybutene viscosity index improver and a methacrylateviscosity index improver, and had a viscosity at 100 F. of 361.8 SSU, aviscosity at 210 F. of 69.7 SSU, and a viscosity index of 141.5.

The composition of Example IV above, was then subjected to a wear testin comparison with a similar lubricating oil composition containing thesame viscsosity index improvers, 4.0 vol. percent of detergent additive(same as in Example I), and 0.7 vol. percent of a commercial dialkyldithiophosphate. The commercial dithiophosphate was a concentrate of 26percent diluent oil and 74 volume percent of a zinc dialkyldithiophosphate in which 65 percent of the alkyl groups were derivedfrom C oxo alcohols and 35 percent were derived from isobutanol. Theweight amount of the commercial zinc dialkyl dithiophosphate used in thecomparison oil was equal to the weight amount of zinc dimethyldithiophosphate in the composition of Example IV. Thus, the compositionof Example IV and the comparison composition were comparable, butdiffering in the nature of the dithiophosphate.

. The wear tests were run in a cam and tappet rig at temperatures in therange of to F. and spring pressures of 280 to 300 pounds. The cam andtappet rig consists of a small section of a Chevrolet V-8 engine block,including the front two camshaft bearing holders and the guides for fourtappets, in which are mounted the front quarter of a camshaft and fourtappets. Two frames for holding push rods and valve springs are mounteddirectly above the tappets in the normal V configuration. Provision ismade for mounting two sets of springs, one above the other, if desired,to allow loadings up to about 700 pounds. Normal tappet loading for aChevrolet engine is about 225 pounds and runs up to about 425 pounds insome larger engines.

The bottom and ends of the block are closed with steel plates, forming acontainer for the test oil in which the camshaft and tappets are totallyimmersed. The hydraulic mechanisms are removed from the tappets, sincethere is no oil pressure to operate them. The camshaft is driven by atwo-horsepower electric motor at about 1740 r.p.m. Heat can be appliedto the bottom by means of strip heaters, and cooling by water circulatedthrough the normal water jacket.

For studying normal wear, spring pressures of about 280 to 300 poundshave been found quite satisfactory, giving fairly sizable andreproducible wear in either 40 or 80 hour tests. The results obtained onoils of known field performance rate the oils in their proper order. Thetests are normally run at 70 to 80 F. using cooling water to carry offfrictional heat, because this appears to be a somewhat more severecondition than higher temperature operation.

The results of the tests are given in Table I. They show that theadditive of the present invention is much more efiective than thecommonly used commercial zinc dialkyl dithiophosphate, which hasheretofore been considered the best available antiwear agent forcrankcase lubricant formulation.

Table 1 Combined Cam and Tappet- Wear in Lubricant 10- Inch 40 Hours 80Hours Example IV Composition of Present In.vention 22.0 251. 0Composition Containing Commercial Zinc Dialkyl Dithiophosphate 25. 753S. 0

As demonstrated by the above table, the products of the invention aremore eilective than the best available prior art material of thisnature. Furthermore, the sols of Examples I to IV were all stable,showing no separation upon standing.

The preceding examples are illustrative of the invention and other knowndetergent additives for motor oil can be utilized in forming theprotective sol. For example, Example I can be repeated, but a P 8treated polyisobutylene of the type previously described in said exampleis used as the suspending detergent in place of the detergent additiveof Example I.

As still another example of the invention, Example I is exactly repeatedbut in place of the 500 grams of detergent additive, 500 grams of aconcentrate is used consisting of 40 weight percent of the neutralcalcium salt of mono-dodecyl benzene sulfonic acid in 60 weight percentmineral lubricating oil. 5 wt. percent of the resulting colloidal solproduct can then be added to wt. percent of a mineral lubricating oilhaving a viscosity of 55 SUS at 210 F. to thereby improve theload-carrying and anti-wear properties of said lubricating oil.

In brief, the specific examples of detergents shown represent preferreddetergent materials, but any detergent which will suspend the metaldialkyl dithiophosphate in a colloidal form in oil can be used.

What is claimed is:

1. An oil composition comprising a major amount of lubricating oil,about 0.1 to 20.0 wt. percent of a mineral lubricating oil detergentadditive, and about 0.01 to 5.0 wt. percent of a metal dialkyldithiophosphate, wherein each alkyl group has 1 to 3 carbon atoms andwherein said metal dialkyl dithiophosphate is water insoluble and isformed in the presence of said detergent additive.

2. An oil composition according to claim 1, wherein said detergent is anorganic alkaline earth metal sulfonate.

3. An oil composition according to claim 1, wherein said detergentadditive is a metal salt of an alkyl phenol sulfide.

4. An oil composition according to claim 1 wherein said detergent isphosphosulfurized polyisobutylene.

5. An oil composition as defined according to claim 1 wherein said metalis zinc.

6. An oil composition as defined according to claim 1 wherein said metalis lead.

7. A lubricating oil composition comprising a major amount of minerallubricatng oil, about 0.1 to 2.0 wt. percent of metal dialkyldithiophosphate and about 1.0 to 10.0 wt. percent of a minerallubricating oil detergent additive wherein said metal dialkyldithiophosphate is water insoluble and is prepared in the presence ofsaid detergent additive by the reaction of dialkyl dithiophosphoric acidand a metal salt, and wherein each alkyl group contains 1 to 3 carbonatoms.

8. An oil concentrate consisting essentially of mineral lubricating oil,about 2 to 14 wt. percent of metal dialkyl dithiophosphate and about 10to wt. percent of a detergent additive, wherein said metal dialkyldithiophosphate is water insoluble and is formed in the presence of saiddetergent additive by the reaction of a dialkyl di thiophosphoric acidand a metal salt, and wherein each alkyl group contains 1 to 3 carbonatoms.

9. An oil concentrate as defined according to claim 8 wherein said metalis zinc.

10. An oil concentrate as defined according to claim 8 wherein saidmetal is lead.

References Cited in the file of this patent UNITED STATES PATENTS2,361,746 Cook et a1. Oct. 31, 1944 2,369,632 Cook et a1. Feb. 13, 19452,824,836 Smith et al. Feb. 25, 1958 2,838,555 Goldsmith June 10, 19582,956,018 Carlyle et al. Oct. 11, 1960 3,018,247 Anderson et al. Jan.23, 1962 OTHER REFERENCES Larson: The Performance of ZincDithiophosphates as Lubricating Oil Additives in Scientific Lubrication,August 1958. Page 15 relied on.

1. AN OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF LUBRICATING OIL,ABOUT 0.1 TO 20.0 WT. PERCENT OF A MINERAL LUBRICATING OIL DETERGENTADDITIVE, AND ABOUT 0.01 TO 5.0 WT. PERCENT OF A METAL DIALKYLDITHIOPHOSPHATE, WHEREIN EACH ALKYL GROUP HAS 1 TO 3 CARBON ATOMS ANDWHEREIN SAID METAL DIALKYL DITHIOPHOSPHATE IS WATER INSOLUBLE AND ISFORMED IN THE PRESENCE OF SAID DETERGENT ADDITIVE.